Swedish activist Greta Thunberg joined calls on the 50th anniversary of Earth Day on Wednesday for a combined effort to tackle the coronavirus pandemic and the climate crisis.
Dramatic improvements in air and water quality as coronavirus lockdowns have cut pollution have prompted calls for a low-carbon future, but the need to get millions back to work is clouding the environmental picture.
With economies round the world shut down, wildlife has returned to city streets, with wolves, deer and kangaroos spotted on thoroughfares usually teeming with traffic.
Fish have been seen in Venice canals no longer polluted by motor boats, while residents of some Indian cities have reported seeing the Himalayas for the first time in decades.
Satellite imagery has shown significant air quality improvements across Europe and Asia, including China, where the coronavirus pandemic emerged.
But residents in some of China's most smog-prone cities said they feared that blue skies would not last as the world's second biggest economy got back to work.
"In the second half of the year, when the epidemic eases, the weather will slowly be worse after factories reopen," said Tang Zhiwei, 27, a resident of Shanghai. "Try your best to enjoy the blue sky now."
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Thunberg said action to tackle coronavirus did not mean the climate crisis had gone away.
"Today is Earth Day and that reminds us that climate and the environmental emergency is still ongoing and we need to tackle both the corona pandemic ... at the same time as we tackle climate and environmental emergency, because we need to tackle two crises at once," she said.
UN chief Antonio Guterres urged governments in an Earth Day message to use their economic responses to the pandemic to tackle the "even deeper emergency" of climate change.
With global battle lines emerging between investors backing "green stimulus" measures and industry lobbyists aiming to weaken climate regulations, Guterres cautioned governments against bailing out heavily polluting industries.
"On this Earth Day, all eyes are on the COVID-19 pandemic," Guterres said. "But there is another, even deeper emergency, the planet's unfolding environmental crisis."
Peter Betts, a former lead climate negotiator for Britain and the European Union, said there was now pressure for coronavirus economic stimulus packages to be "low-carbon, climate-smart".
"A risk, clearly, is that for some governments around the world there will be a huge premium on getting the economy moving, getting people back into jobs," Betts, now with the Chatham House think-tank in London, told Reuters Television.
That is a priority for U.S. President Donald Trump, who wants to get America, and in particular its oil and gas industry, back to work.
"We will never let the great U.S. Oil & Gas Industry down," Trump tweeted, calling for "a plan which will make funds available so that these very important companies and jobs will be secured long into the future!"
Hottest on record
The environmental stakes were rising even before the pandemic's economic shutdown raised hopes in some quarters of a low-carbon future.
Last year was the hottest on record in Europe, extending a run of exceptionally warm years driven by unprecedented levels of heat-trapping greenhouse gases in the atmosphere, according to a study released on Earth Day.
Of Europe's 12 warmest years on record, 11 have occurred since 2000, the European Union's Copernicus Climate Change Service (C3S) said.
"This warming trend is now unequivocal anywhere on the planet. And as a consequence of that, the frequency of these record breaking events is going up," C3S director Carlo Buontempo told Reuters.
The coronavirus pandemic is expected to drive carbon dioxide emissions down 6 percent this year, the head of the World Meteorological Organization (WMO) said, in what would be the biggest yearly drop since World War Two.
But that will not stop climate change, the WMO said.
"COVID-19 may result in a temporary reduction in greenhouse gas emissions, but it is not a substitute for sustained climate action," the WMO said in an Earth Day statement.
With millions staying home, air quality has improved in China. Shanghai saw emissions fall by nearly 20 percent in the first quarter, while in Wuhan, where the pandemic originated, monthly averages dropped more than a third.
But experts worry the decline could give China leeway to turn a blind eye to pollution in order to stimulate the economy, which declined for the first time on record in the first quarter.